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<div class="titlepage"><div><div><h3 class="title">
<a name="iterator.utilities.iterator_traits"></a><a class="link" href="iterator_traits.html" title="Iterator Traits">Iterator Traits</a>
</h3></div></div></div>
<p>
        <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">iterator_traits</span></code> provides access to five
        associated types of any iterator: its <code class="computeroutput"><span class="identifier">value_type</span></code>,
        <code class="computeroutput"><span class="identifier">reference</span></code>, <code class="computeroutput"><span class="identifier">pointer</span></code>, <code class="computeroutput"><span class="identifier">iterator_category</span></code>,
        and <code class="computeroutput"><span class="identifier">difference_type</span></code>. Unfortunately,
        such a "multi-valued" traits template can be difficult to use in
        a metaprogramming context. <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">iterator</span><span class="special">/</span><span class="identifier">iterator_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
        provides access to these types using a standard metafunctions_.
      </p>
<h3>
<a name="iterator.utilities.iterator_traits.h0"></a>
        <span class="phrase"><a name="iterator.utilities.iterator_traits.synopsis"></a></span><a class="link" href="iterator_traits.html#iterator.utilities.iterator_traits.synopsis">Synopsis</a>
      </h3>
<p>
        Header <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">iterator</span><span class="special">/</span><span class="identifier">iterator_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>:
      </p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Iterator</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">iterator_value</span>
<span class="special">{</span>
    <span class="keyword">typedef</span> <span class="keyword">typename</span>
      <span class="identifier">std</span><span class="special">::</span><span class="identifier">iterator_traits</span><span class="special">&lt;</span><span class="identifier">Iterator</span><span class="special">&gt;::</span><span class="identifier">value_type</span>
    <span class="identifier">type</span><span class="special">;</span>
<span class="special">};</span>

<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Iterator</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">iterator_reference</span>
<span class="special">{</span>
    <span class="keyword">typedef</span> <span class="keyword">typename</span>
      <span class="identifier">std</span><span class="special">::</span><span class="identifier">iterator_traits</span><span class="special">&lt;</span><span class="identifier">Iterator</span><span class="special">&gt;::</span><span class="identifier">reference</span>
    <span class="identifier">type</span><span class="special">;</span>
<span class="special">};</span>

<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Iterator</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">iterator_pointer</span>
<span class="special">{</span>
    <span class="keyword">typedef</span> <span class="keyword">typename</span>
      <span class="identifier">std</span><span class="special">::</span><span class="identifier">iterator_traits</span><span class="special">&lt;</span><span class="identifier">Iterator</span><span class="special">&gt;::</span><span class="identifier">pointer</span>
    <span class="identifier">type</span><span class="special">;</span>
<span class="special">};</span>

<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Iterator</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">iterator_difference</span>
<span class="special">{</span>
    <span class="keyword">typedef</span> <span class="keyword">typename</span>
      <span class="identifier">detail</span><span class="special">::</span><span class="identifier">iterator_traits</span><span class="special">&lt;</span><span class="identifier">Iterator</span><span class="special">&gt;::</span><span class="identifier">difference_type</span>
    <span class="identifier">type</span><span class="special">;</span>
<span class="special">};</span>

<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">Iterator</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">iterator_category</span>
<span class="special">{</span>
    <span class="keyword">typedef</span> <span class="keyword">typename</span>
      <span class="identifier">detail</span><span class="special">::</span><span class="identifier">iterator_traits</span><span class="special">&lt;</span><span class="identifier">Iterator</span><span class="special">&gt;::</span><span class="identifier">iterator_category</span>
    <span class="identifier">type</span><span class="special">;</span>
<span class="special">};</span>
</pre>
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<td align="right"><div class="copyright-footer">Copyright © 2003, 2005 David Abrahams Jeremy Siek Thomas
      Witt<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at &lt;ulink url="http://www.boost.org/LICENSE_1_0.txt"&gt;
        http://www.boost.org/LICENSE_1_0.txt &lt;/ulink&gt;)
      </p>
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